Dear @Jason.Jonkman ,
Is there any doc to read in order to know how you linearize the mooring line stiffness matrix ?
Thank you in advance
Hi Riad,
I use pyMAP to linearize the mooring system’s stiffness matrix. pyMAP is the python version of Map++. And it can read OpenFAST primary file (.fst) where Map++ primary file is included. I feel it is convenient to use pyMAP to output mooring stiffness matrix.
You can download and install pyMAP from below link:
https://github.com/WISDEM/pyMAP/tree/dev
Below link is a example how to extract mooring stiffness matrix using fst file:
https://github.com/WISDEM/pyMAP/blob/dev/examples/Ex3_StiffnessMatrixFromFST.py
1 Like
Dear @Ran.Tu ,
Thank u for your suggestion. I will try it 
Dear @Jason.Jonkman,
I notice also that in “Definition of the floating system for phase iv of oc3”, you said that OC3 is held by 3 catenary mooring lines of type “crowfoot” (delta connection).
But when i run map input file, it appears as no delta connection and its simply one line from the fairlead to the anchor.
Is it correct? Could you explain why you did this ?
The photo where the mooring lines appear is below:
Thank you in advance
Riad
Dear @Riad.Elhamoud,
When the OC3-Hywind spar was first modeled in FAST v7, the quasi-static mooring line model used by FAST v7 was simplified and only permitted lines that connected from the floating platform to the seabed, without line-to-line interconnections such as delta connections. Instead, the yaw stiffness associated with the delta connection of the mooring system was considered by adding a yaw spring to the FAST v7 model. Of course, line-to-line interconnections are possible to simulate in MAP++ and MoorDyn within FAST v8 and OpenFAST, but some implementations of the OC3-Hywind spar model still make use of the old FAST v7 convention.
Best regards,
Dear @Jason.Jonkman,
I was wondering if there would be a significant difference in the system response if I compute the mooring system stiffness matrix with pyMAP or Moordyn (Quasi-static - Dynamic approach).
Thank you for your help.
Best,
Busra
Hi @Busra.Yildirim,
The differences between quasi-static and dynamic modeling of mooring systems depends on your system. If there are minimal platform/mooring motions then the effects between the two will be negligible. However quasi-static models neglect the hydrodynamic and inertial responses of the lines so if the platform and mooring system is moving significantly MoorDyn will be a more accurate model.
The original MoorDyn paper introduction has a good explanation of the two modeling approaches: https://www.sciencedirect.com/science/article/pii/S0029801815002279
Hi @Ryan.Davies,
Thank you for your response and the explanation. Is there any Python wrapper or example of how to compute mooring stiffness with Moordyn like above for MAP++ or should I set it up manually? (zero added mass and linearization etc)
Best,
Busra
@Busra.Yildirim if you are looking to use the version of MoorDyn in OpenFAST, the best I can do is point you towards the MoorDyn python driver in the regression tests: r-test/modules/moordyn/py_md_5MW_OC4Semi/py_md_driver.py at main · OpenFAST/r-test · GitHub
I have not used this so I can’t offer too much help into its specifics. If you are looking to only use MoorDyn external from OpenFAST, it does exist as a standalone C++ code with a Pypi package: moordyn · PyPI